Process of hardening alloy steels



United States Patent f 3,222,229 PROCESS OF HARDENING ALLOY STEELS Robert Pribyl, Linz (Danube), Austria, assignor to,

Vereinigte Osterreichische Eisenund Stahlwerke Aktiengesellschaft, Linz.(Danube), Austria, a firm N0 Drawing. Filed July "30,1963, Ser. No. 298,585 Claims priority, application :Austria, July 14, 1960, A 5,429/60 10 Claims. (Cl. 148143) This application. is. a continuation-in-part of my c0- pending application Serial No. 122,087 fi-led lulyo, 1961, now. abandoned,.for. Process of Hardening Alloy-Steels.

This invention relates tohardening-alloy steels, which contain. about 02-08% carbon, .0.2-1%. silicon, 0:3-"2% manganese, 2.1%. chromium. and, if .desired, any or several of the .followingcomponentsz. 0.23%.mo1ybdenum, 01-08%. vanadium,..up.to. 9% tungsten, 11p to 2% cobalt, up to 2% nickel, up to 0.5% titanium and up to 0.5% zirconium.

Most of the steels having these composition ranges are called hot-working steels and are used to make hotduce the life of the tool, and cause the formation of very unclean surfaces on the workpieces.

In order to resist the mechanical andthermal stresses, hot-working steels must have certain performance properties, such as high-temperature stability, high-temperature wear resistance, high-temperature toughness, retention of hardness and freedom from heat cracks. Depending on the nature of the stress, main emphasis must be placed, on one property or the other, because it is not possible to combine all the above properties, part of which are mutually inconsistent, in. a steel to anequal degree.

These required performance properties can be obtained in steels only if certain alloying elements are used. It is usual to employ chromium, molybdenum, vanadium and tungsten. Molybdenum and tungsten can be substituted either entirely or in part for each other. Nickel is sometimes used to increase toughness. Manganese-silicon steels are often used for lower-grade.hot-working.

tools.

According to the present state of the art, thesehotworking steels are hardened, that is, heated and then quenched, only in oil or air. More particularly, as in the case of hot rolls, hardening these steels by water quenching has been impossible owing to the presence and degree of the alloying elements and to the generally large cross-section of suchrolls. Thus within these large rolls, water quenching creates sudden, sharp temperature gradients which cause severe internal stresses leading to warping and cracking during treatment.

In accordance with the invention, steels having alloy compositions within the range of 02-08%. carbon, O.2l% silicon, 0.32% manganese and 2.1 5% chromium, are rapidly-heated by any suitable means, to a surface temperature equal to or exceeding the hardening temperature for the. specific alloy composition. The steels so heated are subsequently quenched in water, which may be preheated. More particularly, a large steel tool, having an alloy composition within the range stated, can be thoroughly heated to a moderate, uniform temperature. After the tool hasbeen uniformly heated the surface of thetool is quickly raised-to a'temperature equal to or greater than the hardening temperature for the specific alloy composition. Water quenchingandsubsequent tempering complete the process. The tool can be tempered in-afurnace, orthe like,-at suitable temperatures for 60 hours-or more to'relieve quenching stresses and recover a limited degree of toughness and ductility.- The entire process is accomplished without cracking or warping the' tool, which-would ordinarily occur if the tool was water quenched according to conventional methods of-treatment.

Hardening in water results invery high'strength tools. For this reasonwater-hardened steels of-the composition described can be more highly tempered, to achieve a certain strength, than tool-s hardened by the conventional oil or air quenching treatment.

changes, so that a higher resistance to the formation of heat cracks and consequently an increase of the life of the tool is achieved. The surface quality of-thehotformed workpiece is-also increased;

Practical experiments with hot rolls have proved that hardening steels according to the invention improves the quality of the material. heat to the workpiece permits-the surface of the steel to be heated above the usual hardening temperatures without detrimental overheating or cracking, w-hich would ordinarily occur if the high temperature deeply penetrated the workpiece. be arranged, whereby the surface orthe -workpiece can be raised quickly-to a temperature above the usual hardening temperature. The temperature inerease beyond the usual value results in a particularly far-reaching solution a of the carbides, whichare-abundantly-present in any hot working steel, to improve the-retentionof hardness. This improvement will be retained even when the 1 increasedtemperature is allowed to-drop to the-usual value before quenching.

Detailed information concerningthardening temperatures for specific steel compositions is available in handbooks, industrial standards such as SAE Iron and Steel TR-30, page 190, specifications providedbysteel' suppliers, and textbooks as, for example, page.301' of the book Tool Steels by Gill, published in 1944 by the American Society for Metals, Cleveland, Ohio.

By experiments it has surprisingly;been'possible to prove that even heavy hot rolls having, for example, a

barrel diameter of 760 mm. and'a weight. of 63501kg. and a composition of 0.40.5% C, 0.250.35% Bi, 0.5-- 0.8% Mn, 2.83.3% Cr and 01-03% V can be quenched with water without dangerof cracking when they have been heated to the hardening temperature very rapidly by means of gas-oxygenburnersor the like.

A preferred embodiment of the invention may be applied to a workpiece having an alloy composition containing 0.4-0.5% C, 0.25-0.35 Si, (LS-0.8% Mn and2.8 3.3% Cr. The steel workpiece is thoroughly: anduniformly heated to between 350 C. and 400 C. ina furnace before surface heating. Surface heating is quickly applied by a burner, an electric device, or the like, raising the workpiece surface temperature to between 950? C. and 1010 C. Means may also be used to feed the ,workpiece at a rate between 37 min/min. and 50 mm./min. to the burner during the surface heating step. Acoolingstep, following the surface heating step reduces the workpiece temperature to the range of 860 C. to 910 C. The cooled workpiece is quenched in water having a temperature between 4 C. and 10 C. Stresses causedby quenching are relieved by tempering in a furnace with air circulation for 24 to 36 hours between 400 C. and 630 C.

Patented. Dec. 7, 1965...

The higher tempering is known to improve the resistance to cyclic temperature 2 The superficial application of Before hardening, preheating may The final portion of the tempering step can be carried out during a period of 36 hours at between 450 C. and 640 C.

The following are typical examples of the process:

EXAMPLE I Hardening of a hot roll for rolling aluminum (1) Heating the roll in a furnace thoroughly to 400 C. (2) Hardening:

Heating the roll by means of a burner to 1010 C. Feeding speed, 37 mm./min. Quenching at a temperature of 900 C. by Water having a temperature of C. (3) Tempering: in a furnace with air circulationfor 24 hours at 520 C. and for 36 hours at 530 C. (4) Hardness after tempering 68-70 Shore-D.

EXAMPLE II Hardening of a roll for rolling copper, zinc, tin, brass, lead (1) Heating of the roll in a furnace thoroughly to 350 C. (2) Hardening:

Heating of the roll by means of a burner to 1000" C. Quenching at 890 C. with water having a temperature of 8 C. (3) Tempering in a furnace with air circulation for 36 hours at 460 C. and for 36 hours at 520 C. (4) Hardness after tempering 70-72 Shore-D EXAMPLE III Hardening of a mandrel for manufacturing of gas bottles by hot drawing Size:

First diameter mm 262 Second diameter mm 222 Length mm 250 Composition of the steel:

C percent 0.43 Si do 0.28 Mn do 0.55 Cr do 3.1 Mo do 0.48 V do 0.20

STEPS (1) Heating of the mandrel in a furnace thoroughly to 4 (2) Hardening:

Heating of the workpiece by means of a burner to 980 C. Quenching temperature 910 C. Quenching with water having a temperature of 5 C. (3) Tempering: in a furnace with air circulation for 24 hours at 630 C. and for 36 hours at 640 C. (4) Hardness after tempering 64-66 Shore-D EXAMPLE IV Hardening of a mandrel for hot drawing Size:

Diameter mm 202 Length mm 1,775 Composition of the steel:

C percent 0.50 Si do 0.25 Mn do 0.70 Cr do 3.0 Mo do 0.51 V do 0.29

STEPS 1) Heating of the workpiece in a furnace to 350 C. (2) Hardening:

Heating of the mandrel to 980 C. Feed speed, 50 mm./min. Quenching at 910 C. by water having a temperature of 4 C. (3) Tempering: in a furnace having air circulation for 24 hours at 630 C. and for 36 hours at 640 C. (4) Hardness after tempering 6365 Shore-D The economic advantages of the invention are substantial, owing to the high cost of the alloy steels concerned. The invention also results in improved tool and hot-formed workpiece quality, particularly when the surface hardening process is carried out with gas-oxygen burners, or electric devices, in combination with the feed hardening and the circulation and feed hardening methods. The resulting reductions in cost increase with the size of the workpieces to be hardened. The process, moreover, does not impose an upper limit on the size and cross-section of the workpieces. As a result, the invention is applicable with special advantages to articles which have a cross-section larger than about square centimeters.

As is apparent from the foregoing, the present invention provides a method for water quenching large steel tools and thelike, having an alloy composition within a specific range to produce a superior, more durable product. While representative embodiments of the present invention have been shown and described for purposes of illustration, various modifications may be made therein as pointed out above without departing from the principles of this invention. Therefore, all such changes and modifications are included within the intended scope of the invention as defined by the following claims.

I claim: 1. A process for hardening alloy steels comprising the steps of preparing a workpiece having a cross-sectional area extending 100 square centimeters and consisting essentially of 0.4-0.55% C, 0.25-0.35% Si, 0.50.8% Mn, 2.83.3% Cr and the balance iron,

surface heating said workpiece to a surface temperature at least as great as the hardening temperature for the alloy steel,

quenching said workpiece in water, and tempering said workpiece.

2. A process for hardening alloy steels as defined in claim 1 wherein said workpiece is at a temperature between 860 C. and 910 C. when it is quenched in water.

3. A process for hardening alloy steels as defined in claim 1 wherein said workpiece is preheated at a temperature substantially below the hardening temperature for the steel alloy composition prior to the step of surface heating said workpiece.

4. A process for hardening alloy steels as defined in claim 3 wherein said workpiece is preheated to a temperature between 350 C. and 400 C.

5. A process for hardening alloy steels as defined in claim 4 wherein said workpiece is tempered at a temperature between 400 C. and 640 C. for a period of from 24 to 60 hours.

6. A process for hardening alloy steels as defined in claim 1 wherein said workpiece is surface heated to a surface temperature between 950 C. and 1010 C.

7. A process for hardening alloy steels as defined in claim 6 wherein said workpiece is cooled to a temperature between 860 C. and 910 C. after the step of surface heating and before the step of quenching said workpiece.

8. A process for hardening alloy steels as defined in claim 7 wherein said workpiece is tempered at a temperature between 400 C. and 640 C. for a period of from 24 to 60 hours.

9. A process for hardening alloy steels as defined in 6 claim 8 wherein said workpiece is preheated uniformally to a temperature between 350 C. and 400 C. before the step of surface heating said workpiece.

10. A process for hardening alloy steels as defined in claim 9 wherein said workpiece is quenched in water at a temperature between 4 C. and 10 C.

References Cited by the Examiner OTHER REFERENCES Tool Steels by Gill, 1944, published by the A.S.M., pages 189, 190, 300, 301, 306 and 482 relied upon.

DAVID L. RECK, Primary Examiner. 

1. A PROCESS FOR HARDENING ALLOY STEELS COMPRISING THE STEPS OF PREPARING A WORKPIECE HAVING A CROSS-SECTIONAL AREA EXTENDING 100 SQUARE CENTIMETERS AND CONSISTING ESSENTIALLY OF 0.4-0.55% C, 0.25-0.35% SI, 0.5-0.8% MN, 2.8-3.3% CR AND THE BALANCE IRON, SURFACE HEATING SAID WORKPIECE TO A SURFACE TEMPERATURE AT LEAST AS GREAT AS THE HARDENING TEMPERATURE FOR THE ALLOY STEEL, QUENCHING SAID WORKPIECE IN WATER, AND TEMPERING SAID WORKPIECE. 